1. Field of the Invention
This invention relates to air conditioning systems with reheaters and, in particular, to air conditioning systems with a first and second cooler and a reheater following the second cooler.
2. Description of the Background Art
The invention of air conditioning by Dr. Willis Carrier more than 75 years ago was brought about due to unacceptable moisture levels in the air. The problem plagues us yet today considering indoor air quality or any application where humidity control is required or desired. Since the original air conditioner, it has been known that air conditioning involves the reduction of temperature (sensible heat) and also the reduction of humidity levels (latent heat). The total heat contained in space is the sum of the sensible heat (as indicated by dry bulb temperatures) and latent heat, indicated by wet bulb temperatures which refers to the moisture content in the air.
It is well known that when air is passed through a cooling coil or some other type of cooling device, both temperature and humidity may be reduced. Temperature can be reduced by removing heat from the air and part of the super-heat of the water vapor contained therein. To reduce humidity, it is necessary to condense a part of the water vapor contained in the air. This requires removing heat from the air until the dew point temperature is reached, and then removing further heat to cause condensation of the water vapor. A cooling device thus first acts primarily to remove sensible heat until the dew point temperature has been reached, and then acts to remove the latent heat of the water vapor in the air, condensing the water vapor, resulting in dehumidification.
The operation of a conventional refrigeration system is well understood. A compressor acts to remove vaporized refrigerant from a cooling coil and to increase the pressure on such refrigerant. The compressed refrigerant then passes into a condenser where heat is removed therefrom, causing liquefication of the compressed refrigerant. The liquefied refrigerant is then passed through a metering device wherein the pressure upon it is reduced. Upon entry of the liquid refrigerant into a cooling coil, the refrigerant changes its state from a liquid to a vapor, this action causes a lowering in temperature of the cooling coil and facilitates the absorption of heat by the refrigerant and coil. The vaporized refrigerant is then drawn into the suction side of the compressor and the cycle is repeated. For automatic temperature regulation, a thermostatic expansion valve may be provided having its thermostatic bulb located at the outlet of the evaporating coil. This arrangement acts to admit sufficient refrigerant into the cooling coil to keep such coil substantially full of liquid refrigerant.
In a conventional cooling device, assuming that the heat removal capacity of the cooling device remains fairly constant and that the dew point temperature of the air is likewise fairly constant, the amount of dehumidification caused by such a cooling device will depend upon the temperature of the entering air. For instance, if the temperature of the entering air is at the dew point, substantially all of the heat removal capacity of the cooling device will go towards removal of water vapor. If, however, the temperature of the entering air is substantially above the dew point, the coil must first act to remove sensible heat until the dew point temperature has been reached before condensation of water vapor will begin. The amount of condensation will therefore be considerably less. It follows that by varying the temperature of the air entering the cooling device, the dehumidifying action of such device may be controlled. It also follows from the above, that the reduction of the humidity of the air to a low level will require that the air be cooled to a low temperature. If the temperature of the air is too low, it would be too cold for direct supply to a space to be air conditioned, i.e., it would overcool the space.
The present invention is directed to improving air conditioning systems in a manner which is safe, secure and economical.
It is known to take advantage of thermodynamic principles to adjust for the above problem. U.S. Pat. No. 2,200,118 to Miller teaches pre-cooling, cooling and reheating by a single refrigeration system. An auxiliary evaporator is placed in the conditioning chamber in advance of the main cooling coil, and a condenser associated with the auxiliary evaporator is placed on the down-stream side of such main cooling coil to act as a reheater. A liquid refrigerant is passed through an expansion valve into the auxiliary evaporator wherein part of the refrigerant is evaporated, thereby causing pre-cooling of the air. The mixture of liquid and gaseous refrigerant is then passed into the reheater wherein the vaporized refrigerant is condensed giving off the heat of condensation for reheating the air. The liquid refrigerant from the reheater, which has given off heat and is thus cooled, is subsequently passed into the main cooling coil wherein it is evaporated, thereby causing cooling of the air. It is apparent that the sensible heat from the air upstream of the main cooling coil is being used to reheat the air.
An air conditioning apparatus capable of dehumidifying air with substantially no reduction in dry bulb temperature when conditions require such a treatment is disclosed in U.S. Pat. 2,093,725 to Hull. The invention involves transferring heat from air to be conditioned to a fluid (or secondary refrigerant). The air is then further cooled by an independent instrumentality, at which point condensation and humidification occur. Finally, the heat which has been transferred to the fluid is transferred from the fluid (or from a condenser of the secondary fluid) to the air to reheat the cooled air as desired. By this procedure, sensible heat of the air above the dew point is transferred to the fluid in a first cooling stage and then returned to the air in the reheating stage. The primary refrigerant compressor and condenser do not contact the air to be conditioned.
U.S. Pat. No. 2,286,605 to Crawford teaches an air conditioning system having a first cooling stage primarily for reduction of sensible heat, a second cooling stage primarily for reduction in of latent heat, and a reheating stage to add sensible heat back to the air. The cooling fluid used in the system is water. The invention is directed in part to a novel cooling tower. Water cooled in first and second evaporators is sent to first and second cooling coils for cooling the air. Water vapor removed from the evaporators is compressed in centrifugal compressors and condensed in condensers. Relatively cool water leaving the reheater is used to condense vapor from the evaporator for the second cooling stage. Relatively warmer water from the cooling tower is used to condense vapor from the evaporator for the first cooling stage. The giving off of sensible heat which results in the cooling of the water in the reheater is thus used to aid in cooling the water vapor withdrawn from the second stage evaporator. The reheating stage assists in the cooling action performed in the latent cooling stage. Steam is discharged from steam turbines to drive compressors. Further, heated water from the evaporators is sent to a cooling tower. Subsequently, some of the water inside the cooling tower is sent through the reheater. The amount of sensible heat added by the reheater is substantially equivalent to the latent heat removed in the second cooling stage.
A method and apparatus for cooling and drying air to a very low level of humidity by cooling the air to twenty degrees Fahrenheit is disclosed in U.S. Pat. No. 3,119,239 to Sylvan. Sylvan teaches a method and apparatus by which cooling can be obtained without the expected problem of coil frosting. Air to be conditioned is first passed through an upstream cooling coil having a surface temperature slightly above freezing. A substantial quantity of the moisture in the air is removed therefrom by condensation in liquid form upon the surfaces of the upstream cooling coil. Thereafter, a sufficient quantity of air at a temperature substantially below freezing obtained from downstream of the downstream cooling coil is mixed with the precooled and dehumidified air so that the temperature of the combined air is below freezing resulting in part of the moisture forming snow and frost particles without physically contacting the heat exchanger surface. This cooled air containing snow and frost particles is then passed through a downstream cooling coil having a surface temperature well below freezing to further cool the air whereby the frost and snow are separated from the air stream. The two cooling coils are in a single loop with a single compressor, the differences in temperature between the first and second cooling coils is attributable to differences in pressures. Hot gaseous refrigerant is provided from the compressor discharge to a reheat coil. The process and apparatus of Sylvan thus concern a first condensation step and a second freezing step, with no provision for a step of reducing only sensible heat.
Finally, U.S. Pat. No. 3,402,564 to Nussbaum et al discloses an air conditioning apparatus for two-stage cooling and dehumidification, wherein gaseous refrigerant from the compressor is used in reheating conditioned air. Instead of being returned to the compressor, refrigerant leaving the reheater is fed directly to a pair of evaporators.
As illustrated by the background art, efforts are continuously being made in an attempt to improve air conditioning systems. No prior effort, however, provides the benefits attendant with the present invention. Additionally, the prior patents and commercial techniques do not suggest the present inventive combination of component elements arranged and configured as disclosed and claimed herein.
The present invention differs from the above air conditioning systems in that, in the present invention, it is the latent heat which is used to reheat the air. This is particularly advantageous since the amount of reheating after dehumidification is a function of the amount the air is cooled below the dew point, which in turn is a function of the humidity present in the air and the amount of humidity to be removed from the air, and not a function of the sensible heat in the air to be conditioned.
The present invention achieves its intended purposes, objects, and advantages through a new, useful and unobvious combination of component elements, with the use of a minimum number of functioning parts, at a reasonable cost to manufacture, and employing only readily available materials.
Therefore, it is an object of this invention to provide an apparatus to condition air by lowering its temperature and by reducing its moisture content comprising a conduit having an input end for receiving air to be conditioned and an output end for dispensing condition air; blower means to effect a flow of air to be conditioned from the input end to the output end of the conduit; a cooling member within the conduit adjacent to the input end adapted to initially cool the air flowing therepast to a temperature near saturation, the cooling member having, in association therewith, pipes in a closed first loop with means for circulating a first cooling fluid between the cooling member whereat thermal energy is added to the first cooling fluid and a remote location whereat thermal energy is removed from the first cooling fluid; a condenser within the conduit adjacent to the output end adapted to reheat the air flowing therepast; an evaporator within the conduit between the cooling member and the condenser adapted to further cool the air flowing therepast to lower dew point for temperature reduction and moisture content reduction; a compressor; piping coupling the evaporator, condenser and compressor in a closed second loop, independent of the closed first loop, for circulating a second cooling fluid between (a) the evaporator whereat thermal energy is added to the second cooling fluid, (b) the condenser whereat thermal energy is removed from the second cooling fluid, and (c) the compressor whereat the cooling fluid is compressed.
Another object of the present invention to more efficiently condition air.
It is a further object of the present invention to provide a preliminary and secondary cooling of air to be conditioned followed by a reheating of the conditioned air.
It is a further object of the present invention to couple a second cooling component of an air conditioning system with a reheater.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed as merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiments in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.